CHAPTER 12HUMAN GENETICS

Chromosomal Abnormalities

• 1 infant in 200 newborns has a chromosomal abnormality • 28% of first trimester miscarriages have a chromosomal abnormality

• Abnormalities in larger chromosomes don’t usually survive

Color BlindnessCause:

Mutation in gene on X chromosome

Symptoms:• More common in males

(8% of males are colorblind)• Can’t distinguish certain

colors • Most common = red/green

Can you see the numbers and shapes?

HemophiliaCause:

change in gene on X chromosome that codes for blood clotting protein

Symptoms:• More common in males• Internal and external bleeding•Can result in death•Transfusions & hospitalization are required frequently to stop bleeding!

Cystic Fibrosis• Mutation in gene on chromosome 7

• Symptoms: – More common in Caucasians

– Make extra thick mucous in lungs and pancreas which leads to respiratory and digestive complications

– Salty skin is clue

Achondroplasia(Dwarfism)

Cause: (Autosomal DOMINANT- found on chromosome 4)

Most new mutations in egg or sperm cell, but can be inherited from parent with gene

•1 in 20,000 births

•200,000 “little people” worldwide

•Normal size torso; short arms and legs

DeletionPiece of DNA code is lost

Wolf-Hirschhorn syndrome

• Deletion on arm of chromosome 4

• Mental retardation

• Large low set ears

• Club feet

Cri-du-chat “cry of the cat”• Deletion on arm of chromosome 5• 1 in 50,000 births• More common in girls

• Mewing cry in infancy• Mental retardation

Prader-Willi Syndrome • Deletion in chromosome 15

• Feeding problems: poor weight gain in infancy, won’t eat

• Ages 1-6 excessive, rapid weight gain

Victor at age 1 Victor at age 2

Duchenne Muscular Dystrophy

Symptoms:• Deletion in gene on X chromosome• 1 in 3500 male births• Appears before age 5• Progressive muscle weakening• Most in wheelchair by age 13• Eventually lethal

Jerry Lewis telethon

Non-disjunctionA homologous pair sticks together and doesn’t

separate at MEIOSIS.

One cell gets 2 copies of the chromosome the other cell gets none.

Monosomy- 1 chromosomeTrisomy- 3 chromosomes

Down’s syndrome (trisomy 21)•Most common chromosomal abnormality

•1 in 660 births

•Similar facial features

•Slanted eyes

•Protruding tongue

•Mental retardation

•Risk increases with age of mom

Patau syndrome (trisomy 13)•1 in 7000 births (rare)

•Cleft lip & palate•Eye abnormalities

(too small or missing)

low set ears

polydactyly

Kleinfelter syndrome XXy

•1 in 1000 births

•Male = XXy

•Average to slight decrease in intelligence

•Small testes/can’t have children

•Usually not discovered until puberty when don’t mature like peers

•Has breast tissue & poor beard growth

Turner’s syndrome (X)

• 1 in 5000 births• Female = X• Small size• Slightly decreased

intelligence• Hearing loss common• Undeveloped

ovaries/can’t have children

Xyy syndrome

• Xyy males• Taller, more aggressive• Some early studies showed

greater incidence of Xyy males in prison populations than in the normal population

Substitutions

Can YOU find the difference?

the fat cat ran and ran

the fat rat ran and ran

Sickle Cell Anemia is caused by this.

Sickle Cell Anemia

•Substitution on chromosome #11

A is changed to T

Insertion (addition)Extra Piece of DNA is added to code

Huntington’s • Insertion at end of gene on chromosome 4

• Degenerative brain disorder

• Symptoms appear at age 30-40 (Usually after having children) • Lose ability to walk, think, talk, reason

• 50/50 chance of passing it to childNow there is a test to tell if you have the gene before symptoms appear.Would you want to know?

How can we detect disorders?

Karyotype

•Can tell missing/extra chromosomes•Gender•Some deletions/additions

What is wrong with

this karyotype?

Amniocentesis•Insert needle into sac and withdraw fluid containing baby’s cells

•Done at 14-16 weeks

•Can detect:•Cystic Fibrosis•Huntington’s•missing/extra chromosomes

The End.